Posttranslational modifications of proteins are required for many cellular functions including the mediation of protein-protein interactions, enzymatic activity, degradation, localization of proteins to cellular compartments and maintenance of stability. Ubiquitination, one type of protein modification, occurs when the protein ubiquitin becomes ligated to a target protein. The attachment of one or more ubiquitin molecules then signals the destruction of the protein substrate.
Recently a novel family of ubiquitin-like molecules were described which modify proteins by a similar mechanism. Sentrin (also known as UBL1, PIC1, GMP1, and SUMO-1) is the prototype member of the ubiquitin-like family of protein modifiers and was isolated by several labs independently (Boddy et al., Oncogene, 1996, 13, 971-982; Mahajan et al., Cell, 1997, 88, 97-107; Okura et al., J. Immunol., 1996, 157, 4277-4281; Shen et al., Genomics, 1996, 36, 271-279).
Sentrin shows only a slight sequence homology to ubiquitin (18%) and, unlike ubiquitin, the attachment to a protein substrate is reversible and only forms in a one to one stoichiometry with the targeted protein. In addition, Sentrin conjugation results in protein trafficking and localization and not in labeling of target proteins for degradation.
In an effort to identify proteins involved in double strand break repair of DNA, Shen et al. demonstrated that Sentrin interacts with RAD51/RAD52, a protein complex formed during DNA repair and recombination (Shen et al., Genomics, 1996, 36, 271-279).
Other studies isolated Sentrin as a factor which binds to the `death domain` of the TNFR1 receptor and therefore plays a role in apoptosis. These studies showed that when overexpressed, Sentrin provided protection against both Fas/APO-1 and TNF-induced cell death (Okura et al., J. Immunol., 1996, 157, 4277-4281). Northern blot analysis of Sentrin showed ubiquitous expression in all tissues, with the highest levels being in the heart, skeletal muscle, testis, ovary and thymus.
Sentrin was also shown to be involved in nuclear protein import by conjugating to the 70 kD RanGAP1 protein which could then interact with RanBP2 resulting in a complex which is necessary for nuclear protein import (Mahajan et al., Cell, 1997, 88, 97-107). Since then, Sentrin has been shown to conjugate to the mammalian homolog of the UBC9 enzyme, an E2 ubiquitin-conjugating enzyme active during cell cycle progression (Gong et al., J. Biol. Chem., 1997, 272, 28198-28201; Schwarz et al., Proc. Natl. Acad. Sci. USA, 1998, 95, 560-564), and to interact with PML and Sp100, two nuclear dot proteins associated with the development of acute promyelocytic leukemia and primary biliary cirrhosis (PBC) (Boddy et al., Oncogene, 1996, 13, 971-982; Sternsdorf et al., J. Cell Biol., 1997, 139, 1621-1634).
Finally, disclosed in WO98/20038 are claims to the nucleic acid sequences of the human, mouse and yeast Sentrin, antibodies to the Sentrin protein, cell lines or a transgenic animal expressing the protein, methods of detecting said protein with an antibody and methods of detecting the nucleic acid encoding Sentrin. Also claimed are shorter segments of the nucleic acid sequence 14 contiguous nucleotides in length that have the same sequence or are complementary to the Sentrin sequence intended for use as primers, probes, and templates (Yeh, 1998).
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of Sentrin. Consequently, there remains a long felt need for additional agents capable of effectively inhibiting Sentrin function. Therefore, antisense oligonucleotides may provide a promising new pharmaceutical tool for the effective and specific modulation of Sentrin expression.